What causes swamp cancer?

Not a lot is known about the agent that causes swamp cancer. There aren't many experts on the disease, and even those who consider themselves experts often don't know a ton about it.

What is known is that the infectious agent Pythium insidiosum typically lives in plants that grow near water. When the plants are wet or are submerged in water for whatever reason, it releases zoospores, which are effectively spores that can swim, into the water.

Those zoospores can spread infection by getting into holes on an animal's body as small as a mosquito bite or a scrape. Experts say the disease has a low infection rate, but it can be very difficult to get rid of once it gets into a creature's body.

How does swamp cancer affect the ponies?

It can leave lesions on their bodies. It's thought to be very itchy and potentially even painful for the ponies. However, it is not a true cancer, which alleviates some of the problems traditionally associated with that.

Denise Bowden, spokesperson for the Chincoteague Volunteer Fire Company (which cares for the ponies), was able to sit in on a procedure in which a veterinarian showed her how the disease manifests in a horse's body.

"The little seed like fungus looks exactly like sesame seeds," Bowden wrote. "They bunch up in one area like grapes and then spread to other areas."

Part of the problem with the disease is because the Chincoteague ponies roam the island, people who know what to look for don't see the ponies every day.

"When humans and household pets come in contract with it through a small cut or scrape, it's easy to treat because it's detected early enough," Bowden said in an email. "Our wild ponies go for days without anyone seeing them, so when the issue has been spotted and we bring in the pony, the fungus is running amuck."

Can swamp cancer affect people?

It's very unlikely, but it could theoretically affect people in the same way it does horses. That being said, swamp cancer is not a contagious disease. It also has an incredibly low infection rate, meaning you're probably safe.

How is swamp cancer treated?

Officials at the fire company have not gone into a lot of specifics about how they are treating the disease in the horses, but Bowden estimated initial treatments would cost about $1,500 per pony.

Bob Glass, owner of Pan American Veterinary Labs in Texas and one of the few experts on the disease, said swamp cancer creates an autoimmune response in horses that is similar to an allergic reaction, but the reaction doesn't kill off the pythium in the body.

The disease is notoriously hard to treat, and many veterinary schools still teach it as uncurable, Glass said.

"It used to be considered a curse because there weren't any treatments that really worked," Glass said. "It used to be that owners would spend between $5,000 and $10,000, and the horse would still die."

Glass, working with other experts, helped to develop an immunotherapy treatment similar to a vaccine to help a horse's body instead respond in a way that gets rid of the disease.

Bowden said in October those caring for the ponies were exploring a different treatment, one that involves surgery. She said in more recent Facebook posts that treatment was not working, but a new drug expected to arrive Tuesday will hopefully be more effective.

​​​​​​Reach reporter Hayley Harding by email at hharding@delmarvanow.com or on Twitter @Hayley__Harding.